Methods for Controlling Medical Fluid Injections

ABSTRACT

The present invention is directed to control of medical fluid injection systems. For instance, in some embodiments, an injection protocol may be initiated, and an actual flow rate of the medical fluid utilized in the injection protocol may be adjusted based, at least in part, on an inherent system elasticity of the injection system.

FIELD OF THE INVENTION

The present invention generally relates to injections of medical fluids,and more particularly, to methods for controlling injections of suchmedical fluids.

BACKGROUND

It is well recognized that the appropriate dose for many medications isrelated to a number of variables, including, for example, the size,weight, and/or physiologic state of the patient being treated. Thisvariation is readily apparent from the different recommended doses manymedications have for adults and children. The appropriate dose ofcontrast media for a given medical imaging procedure also tends to bedependent upon the size and weight of the patient being examined as wellas additional factors.

Although differences in dosing requirements for medical imagingprocedures have been recognized, many conventional medical imagingprocedures, including angiographic, computed tomography, magneticresonance and ultrasound imaging, continue to use pre-set doses orstandard delivery protocols for injecting contrast media for medicalimaging procedures. Although using fixed protocols for deliverysimplifies the procedure, providing the same amount of contrast media topatients of varying size and weight can produce very different resultsin image contrast and quality.

It is typically desirable to coordinate the time of the imageacquisition with the time of greatest levels of contrast in the regionof interest, in some instances, with respect to a threshold value. Manyphysiological factors can affect the start time and duration of asufficient level of contrast in the region of interest. For example,because the cardiovascular system generally provides the means forcirculation of contrast agent throughout the body after it is injected,a patient's cardiac output can have a significant effect on thedistribution of the contrast agent as well as the time taken for thecontrast agent to reach a particular organ or vessel.

Current understanding of intravenous contrast enhancement is furthercomplicated by multiple interacting factors. As such, in many respects,contrast enhancement still relies heavily on the experience andintuition of the physician rather than rigorous, quantitative analysisof the mechanism of contrast enhancement.

SUMMARY

In certain embodiments, the present invention relates to systems andmethods for promoting injection of medical fluid at actual flow ratesthat substantially correspond with desired flow rates. In certainembodiments, the present invention relates to systems and methods forpromoting injection of contrast media at flow rates sufficient to enableachievement of desired levels of patient enhancement during imaging. Inthe above-mentioned embodiments, elasticity of the injection system(e.g., various components thereof) is taken into account whencontrolling (e.g., adjusting) the actual flow rate of the injectionsystem so that the desired flow rate and/or patient enhancement can beachieved.

Certain exemplary aspects of the invention are set forth below. Itshould be understood that these aspects are presented merely to providethe reader with a brief summary of certain forms the invention mighttake and that these aspects are not intended to limit the scope of theinvention. Indeed, the invention may encompass a variety of aspects thatmay not be explicitly set forth below.

One aspect of the present invention is directed to a method of operationfor a medical fluid injection system. In this method, an injectionprotocol that includes a desired flow rate for the medical fluid (e.g.,contrast media) is initiated. An actual flow rate of the medical fluidis adjusted to follow the desired flow rate for the medical fluid based,at least in part, on an inherent system elasticity of the injectionsystem.

Another aspect of the invention is directed to a method of operation fora medical imaging system that includes a medical fluid injectionassembly and a medical imaging device. In this method, an injectionprotocol corresponding to a desired level of patient enhancement isinitiated. Based, at least in part, on an inherent elasticity of theinjection assembly, an actual flow rate of the injection protocol isadjusted to achieve the desired level of patient enhancement.

Various features discussed below in relation to one or more of theexemplary embodiments may be incorporated into any of theabove-described aspects of the present invention alone or in anycombination. Again, the brief summary presented above is intended onlyto familiarize the reader with certain aspects and contexts of thepresent invention without limitation to the claimed subject matter.

BRIEF DESCRIPTION OF THE FIGURES

Various features, aspects, and advantages of the present invention willbecome better understood when the following detailed description is readwith reference to the accompanying figures in which like charactersrepresent like parts throughout the figures, wherein:

FIG. 1 shows an exemplary injection profile and a lagging output flowrate.

FIG. 2 shows the exemplary injection profile and an adjusted injectordrive speed to correct the output flow rate.

FIG. 3 shows an exemplary injector having a syringe and injectorcontrol.

FIG. 4 is a flow chart of a method to deliver a specific injectionprofile.

FIG. 5 shows an exemplary CT scanner with a control in communicationwith an exemplary injector.

FIG. 6 is a flow chart of another method to deliver a specific injectionprofile.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of the present invention (E.G., the exemplaryembodiments(s) thereof), the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

Many injection systems used in medical scanning procedures have aninherent elasticity due to compression of an associated syringe plunger,expansion of an associated syringe barrel, and/or expansion ofassociated extension tubing. This elasticity causes the output of theinjection to “smooth out” and lag behind the input. As such, inputspeeds of the syringe plunger may need to be exaggerated in order toproduce the desired output. For example, a pressure increase is requiredto increase the flow rate; however, some of the energy resulting fromthe pressure increase is stored in the elasticity of the system. Tocompensate for this elasticity, the injector will need to increase speedfaster than it would if the system were not elastic in order toaccurately output the desired flow rate. Conversely, in order to reducethe injection rate, the injector must slow down sooner in order to allowfor stored energy to diminish. In extreme cases, the motor may actuallyneed to reverse direction.

Flow rate correction factors for the injector may be determined during atest injection. The injector may sense the type of syringe being used soa predetermined elasticity factor may be saved for each syringe type.During the test injection, the injector may determine parametersinfluencing the output rate of the injector by analyzing a pressureprofile produced during the test injection. Correction factors to theinjector motor speed may also be determined based on the analysis of thepressure profile. The injector may analyze the corrected speed(s) of themotor to ensure that it does not exceed the design limits of theinjector.

An exemplary injection protocol may be seen in FIG. 1. This figureillustrates how the actual output flow rate from the injector lagsbehind the desired output of the injection protocol. Using the resultsof the analysis of the pressure profile created during the testinjection, correction factors to the input speed of the drive ram in theinjector may be determined which will allow the output flow rate to moreclosely match the desired flow rate of the injection protocol. Anexample of the correction factors adjusting the drive ram speed may beseen in FIG. 2. The correction factors exaggerate the input drive speedin order to compensate for the energy stored in the inherent elasticityof the injector system and allow the output to more closely follow thedesired flow rate of the injector protocol.

The inherent elasticity of the injector system is related to the syringeand tubing being used. In addition, the viscosity of the contrast mediaand the diameter of the catheter (not shown) affect the output flow rateof the injector. Referring now to FIG. 3, the injector receives asyringe 14, which in turn is connected to a catheter to deliver contrastmedia to a patient. In some embodiments, the syringe that is insertedinto the injector 12 may contain an RF-ID data tag 16, communicatingwith an antenna 18 connected and communicating with the injector 12,which may contain information related to that particular syringe. Forexample, the RF-ID data tag 16 may contain the type of syringe andcontrast media therein. This identification information may allow aninjector control 10 to easily retrieve elasticity data gathered from theanalysis of the pressure profile, created during the test injection. TheRF-ID data tag 16 may also contain data related to the pressure profileand syringe elasticity. In other embodiments, a physician or technicianmay manually enter the syringe and tubing information directly into theinjector control 10. A library of elasticity data for each of thesyringes and tubing that are used with the injector may be stored in theinjector control 10 for later use.

Referring now to FIG. 4, an injector protocol may be selected in block100 that is consistent with the medical procedure performed on a patientwith an imaging system. A syringe containing contrast media is insertedinto the injector. At this point, in block 102, a determination of thetype of syringe, the type of contrast media, and other injectorparameters is made in order to locate elasticity data for the injector.This data may be stored, in some embodiments, in the injector control.Once the type of injector with syringe and contrast has been determined,elasticity data is retrieved in block 104. A series of correctionfactors is determined in block 106 from predictions made based on thedesired output waveform shape and the elasticity data for the injector.The correction factors will be applied to the input drive ram speed inorder to adjust the actual output flow rate, to closely follow thedesired flow rate. The correction factors exaggerate the input drive ramspeed, which may overshoot the actual desired output rates. Exaggeratingthe drive speed of the injector may compensate for the inherent lag inthe fluid. In some situations, this may require that the drive ram speedbe faster than the increase in the desired flow rate of the system. Inother cases, the speed of the drive ram may be slower than the desiredflow rate. In some extreme cases, it may be necessary to reverse thedirection of the drive ram in order to obtain the proper output flowrate profile.

Before the correction factors may be applied to the input drive, a checkshould be done in block 108 to determine if, once the correction factorsare applied, the input drive ram speed is within the design limits ofthe injector. If the drive speed with the correction factors applied isoutside of the design limits of the injector (no branch of decisionblock 108), then the correction factors are adjusted in block 112 to bewithin the design limitations. After these factors have been adjusted,the factors are then applied to the injector protocol in block 110. Oncethe input drive speed has been adjusted so that the desired flow ratemay be met, the injector protocol is ready to be implemented in aninjection to the patient.

System elasticity may be based on many factors related to differentcomponents of the injection system. For example, the compression of thesyringe plunger may contribute to the elasticity as it encounters theincompressible fluid of the contrast media. Similarly, the barrel of thesyringe may contribute to the elasticity of the overall system as thebarrel may expand slightly due to the sudden increase in pressureapplied by the plunger. In addition to the syringe and the plunger,which are part of the injector, extension tubing and catheter tubingconnecting the injection system to the patient may also have an inherentelasticity, allowing the tubing to expand due to the increase in thepressure applied to the contrast media, contributing to the elasticityof the system.

The elasticity of the injector system may be determined from analyzing apressure profile resulting from a test injection. The test injectioninjects a small amount of contrast media into a patient while measuringthe pressure profile. Analysis of this pressure profile enables analgorithm in or communicating with the injector control to predict thelags in the delivery of the contrast media due to the elasticity in thesystem. From these predictions, the speed of the drive ram contactingthe plunger may be adjusted to compensate for the inherent lags. Afterthe pressure profile has been analyzed, the results of that profile andthe components contributing to the elasticity of the system may bestored in the injector control, for example, for later use with otherpatients. Once a library of syringes, injectors, tubing and othercomponents has been built, the need for further test injections may notbe necessary.

In one aspect of the present invention, as discussed above, an injectionprotocol may be selected by a technician or by a physician withexperience in the imaging systems in order to obtain a clear image ofthe portion of the body of the patient of interest. In another aspect ofthe present invention, the imaging system may also be able to sendinjection protocol information to the injector in order to makereal-time adjustments to the injection rate of the contrast media duringan imaging procedure.

Referring now to FIG. 5, an imaging system, such as a CT scanner 20, tobe used in a medical procedure on patient 22 may communicate using acommon interface 26 with the injector 30. A control for the CT scanner24 communicates through the interface 26 to a control for the injector28 in order to increase or decrease the injection rate of the contrastmedia to achieve clear images. In some embodiments, this communicationmay be accomplished through a CAN interface. In other embodiments, otherinterfaces such as RS-232 or RS-422 may be used. As will be apparent tothose skilled in the art, in addition to these three communicationprotocols, any protocol that would allow the injector and the imagingsystem to communicate would be sufficient.

Referring now to FIG. 6, the medical procedure utilizing a CT scannerand an injector begins in block 120. The imaging system used in thisparticular embodiment is a CT scanner, although other imaging systemsmay also be used. In other embodiments, the imaging system may comprisea magnetic resonance imaging system, an angiographic imaging system, oran ultrasound imaging system. During the imaging process in block 122the CT scanner may determine an optimum flow rate of the contrast media.This flow rate is communicated to the injector control through a commoninterface in block 124. After the flow rate information has beencommunicated to the injector control, the type of syringe, contrastmedia and tubing may be determined in block 126. Once the componentshave been identified in block 128, the elasticity data for the injectorsystem may be retrieved. Similar to above, a set of correction factorsis then determined from the component elasticity data and from flow ratedata sent from the imaging system in block 130.

Again, the correction factors are analyzed to determine if they arewithin the design limitations of the injector. If the correction factorswould cause the injector to operate outside of the design limitations,in block 134, these correction factors would be adjusted to be withindesign limitations. The correction factors are then applied to theinjector drive ram speed in block 136 and the output flow rate of theinjector is modified accordingly. If new or additional flow rates areavailable from the CT scanner (yes branch of decision block 138), then anew set of correction factors may be determined based on the new flowrate and the process continues. If no new flow rate information isavailable from the scanner (no branch of decision block 138), then themedical procedure completes with the CT scanner and the injector.

As various changes could be made in the above-described aspects andexemplary embodiments without departing from the scope of the invention,it is intended that all matter contained in the above description shallbe interpreted as illustrative and not in a limiting sense.

1. A method of operation for a contrast media injection system, themethod comprising: initiating an injection protocol comprising a desiredflow rate for the contrast media; and adjusting an actual flow rate ofthe contrast media to follow the desired flow rate for the contrastmedia based, at least in part, on an inherent system elasticity of theinjection system.
 2. The method of claim 1, wherein the adjustingcomprises accounting for elasticity of a syringe plunger.
 3. The methodof claim 1, wherein the adjusting comprises accounting for elasticity ofa syringe barrel.
 4. The method of claim 1, wherein the adjustingcomprises accounting for elasticity of a contrast media container, 5.The method of claim 1, wherein the adjusting comprises accounting forelasticity of extension tubing.
 6. The method of claim 1, furthercomprising predicting the inherent system elasticity for the injectionsystem prior to the adjusting.
 7. The method of claim 6, furthercomprising performing a test injection prior to the initiating.
 8. Themethod of claim 7, wherein the predicting is based, at least in part, ondata from the test injection.
 9. The method of claim 6, wherein thepredicting occurs prior to the initiating.
 10. The method of claim 6,wherein the inherent system elasticity is predicted based, at least inpart, on elasticity data related to a container, syringe, tubing, or acombination thereof utilized in the system.
 11. The method of claim 6,wherein the inherent system elasticity is predicted based, at least inpart, on viscosity data related to the contrast media.
 12. The method ofclaim 1, further comprising calculating the inherent system elasticityusing an algorithm.
 13. The method of claim 1, further comprising:sensing an elastic component associated with the injection system; andretrieving a predetermined elasticity factor for the component.
 14. Themethod of claim 13, where the component comprises a contrast mediacontainer, a syringe, tubing, or a combination thereof.
 15. The methodof claim 13, wherein the sensing comprises reading data from an RF-IDdata tag that contains information about the component.
 16. The methodof claim 15, wherein the information comprises at least one of pressureprofile data and elasticity data.
 17. The method of claim 1, furthercomprising determining a flow rate correction factor for the injectionprotocol based, at least in part, on the inherent system elasticity,wherein the adjusting is based, at least in part, upon the flow ratecorrection factor.
 18. The method of claim 17, wherein the flow ratecorrection factor is dependent upon viscosity of the contrast media. 19.The method of claim 17, wherein the flow rate correction factor isdependent upon catheter size.
 20. The method of claim 1, wherein theadjusting comprises increasing an actual motor speed of the injectionsystem more than a motor speed corresponding with the desired flow rate.21. The method of 1, wherein the adjusting comprises decreasing anactual motor speed of the injection system more than a motor speedcorresponding with the desired flow rate.
 22. The method of claim 1,wherein the adjusting comprises reversing a direction of motion of amotor of the injection system.
 23. The method of claim 1, wherein thedesired flow rate comprises a plurality of flow rates.
 24. The method ofclaim 23, wherein the plurality of flow rates is communicated betweenthe injection system and a medical imaging system via a commoninterface.
 25. The method of claim 24, wherein the common interface is aCAN interface.
 26. The method of claim 24, wherein the common interfaceis an RS-232 interface.
 27. The method of claim 24, wherein the commoninterface is an RS-422 interface.
 28. The method of claim 1, wherein atleast a portion of the injection protocol is carried out during medicalimaging of the patient.
 29. The method of claim 28, wherein the medicalimaging comprises CT scanning of the patient.
 30. The method of claim28, wherein the medical imaging comprises magnetic resonance imaging ofthe patient.
 31. The method of claim 28, wherein the medical imagingcomprises angiographic imaging of the patient.
 32. The method of claim28, wherein the medical imaging comprises ultrasound imaging of thepatient.
 33. The method of claim 28, wherein the medical imagingcomprises optical imaging of the patient. 34-66. (canceled)